Apparatus and method for drying solid material



J.. E. PEIRCE APPARATUS ND METHOD FOR DRYING SOLID MATERIAL Feb. 28g3950 Filed July 14, 1945 NTI \ bnn/UV INVENTOR. a//fvfP/R Patented Feb.28, 1950 y I 2,499,157

UNITED STATES PATENT APPARATUS AND ME'EHOEB FOR DRYNG SOLID M'EERAL JohnE. Peirce, Arlington, N. Ji., assigner to titled Chemicai c DyeCorporation a corporation et' New York Application .Fully M, 11945,Serial No. 605,142

3 Claims. (m. 3dB-1137) i f E This invention relates to apparatus andmethod and the rotary drum. Principally because of apfor treating solidmaterial with a gas, at least preciable eccentric and axial movementl ofthe some of which material exists as dust when in rotary drum, resultingfrom wear and tear land the treated condition. maladjustinent of therotary drum on its sup- The present improvements may be exemplified 5porting rollers and driving gears, it is dilcult in connection withconstruction and operation of and often impossible to provide a gas anddusta rotary drum used to eect the final drying of tight joint betweenthe rotary drum and the xed salts such as anhydrous bisuliite of soda,trisogas inlet. Hence, to avoid dusting at this joint dium phosphate,sodium hyposulte, and sodium it has been the practice to operate theapparabiuoride. In several processes in the chemical tus as a whole insuch a way as to maintain a industry, materials of the nature indicatedare slight negative gas pressure at the material out'- preliminarilydried, e. g. dewatered or separated let-gas inlet end of the dryer. Sucha. procedure from the mother liquor as by a centrifuge, and requires theuse not only of a blower to supply there results a salt containing say3-10% moisgas to the gas inlet end of the dryer but also an ture whichmust be removed before the material additional suction fan in the tailgas line of the is ready for packaging. Final drying is commondryer, theoperation of which fan must be carely eiected by means of a rotary drumand a suitfully adjusted in order to maintain the desired able dryinggas. In the operation of apparatus negative pressure at the materialdischarge-gas of this type, the material to be dried is fed into inletend of the dryer. Often, it is necessary to one end of the drum arrangedso that the maeffect drying by means 0f an inert gas to avoid terialpasses thru the drum to the opposite or oxidation of the material beingdried. In this material outlet end. A drying gas such as heatedsituation, when Operating in accordance with the and nltered air or aheated inert gas such as carprior practice, i. e. maintaining a negativepresbon dioxide, depending upon the particular nasure at the materialoutlet end of the drum, it ture of the operation at hand, is chargedinto the 5 is not possible to avoid drawing in atmospheric materialoutlet end of the drum and iiowed thru air thru the joint between therotary drum and the drum countercurrent to movement of the mathe fixedgas inlet. Further, the atmosphere in terial. Because of their dampcondition as fed many chemical plants contains impurities which into thedrum, such materials present no particuare sucked into the dryer andcause contaminalar dusting problem in that portion of the drying tion of.the product being dried. zone at and near the material inlet-gas outletThis invention aims to provide a. system by end of the dryer. However,as theV material is means of which the foregoing 'difficulties aregradually dried, dusting proportionately ineliminated. The invention,its further objects creases, and in the immediate vicinity of the maandadvantages may be understood from the folteria] discharge end, asubstantial amount of the lowing description .taken in connection withthe material exists in dust form. Because of dustaccompanying drawing,in which Fig, 1 is 8,1011..

ing. depending largely 'upon the diameter of the gitudinal verticalsection of the improved apdryer, it is necessary to supply the treatingeas paratus, and Fig. 2 is a transverse section on the thereto in such away that the gas stream pass- 1in@ 2 2 of Fig 1 ing thru the dryer has avelocity insucient to to Referring to une drawing, it indicates ahorientlaiin an apprECia'ble dust lOad, require-1 Zgnta] cylindricaldrum providing an elongated ment being imposed so as to avoid sweepingdust, drying chamber H, The drum is mounted for constituting anappreciable portion of the dry mtaticn on rollers g2 and tracks g3, andis D'dlt, 0u? 0f the dryer along Wlth the Spent equipped with suitabledriving gear not shown gaSffOllS dlylng agem- Thus for dryer 0f glYen 45associated with a source of power. Damp matedeslgn the v eloclty 0f thetreatmg gas Passmg rial to be dried may be fed continuously by a starthru the dI-Vmg Chamber musf be held below or feeder i5 into a chamberi6 having at the botat not more than @gwen maxmumtom a ribbon conveyoril. Introduction of ma- In the constructmn. of dryers of the kind un-,terial into chamber i@ may be Such that the del Consideration, thetreating 0I' drying gas is 50 level of material is maintained at aboutor beusually fed into the drum from a gas bustle 01 low the axis of theconveyor i'i so as to provide vestibule communicating with the source ofgasa, free space thru which spent drying gas enters ecus drying agent.As previously stated, the atchamber it forv discharge from the apparatusmosphere' at the solid material diScharge-drythru outlet 2i.v The drumis pitched slightly toing gas inlet end of the dryer is substantiallyward the gas inlet end which pitch in conjuncdust-laden. Because of thiscondition, and the tion with longitudinal nights 22 serves to move factthat the dryer proper is rotary and the gas the material thru chamberit. vestibule is fixed, in the prior practice it has been A source ofgaseous drying medium 23 is concustongary to attempt to providegas-tight joints nected .to the suction side of a blower 2d which at.the connection between the xedgas bustle forces the gas successivelythru a suitable purifier 26 and a heater 21, the discharge pipe 28 ofwhich` is provided with a valve 29 and opens into the fixed gas inletchamber or vestibule indicated generally by 30.

According to the present invention, it is not necessary to attempt toprovide a gas and dusttight joint at the connection between the fixedgas chamber 30 and the rotary drum I0. The construction and operationafforded are such, notwithstanding the requirement of maintaining in thedrying chamber I I a relatively low gas velocity, as to prevent thepresence of dust at the gas inlet opening of the drum and at theconlnection between the drum and the fixed gas inlet chamber. On theside adjacent the rotary drum, chamber 30 is provided with aA circularcut-out 32 having a diameter appreciably greater than the outsidediameter of the drum neck 33 which projects into chamber 30 and forms agas inlet opening 34 for the drum. If desired neck 33 maybe providedwith an outwardly projecting flange 35. As shown on the drawing, therelation of drum neck 33 and flange 35 on the one hand and circularcut-out 32 on the other is such as to permit appreciable eccentric andaxial movement of the drum neck without a metal-tometal contact and thusaffords a non-gas-tight joint connection between the drum and the gaschamber.

In accordance with the invention, the area of the gas inlet opening 34of the drum is chosen, relative to the cross-sectional area of dryingchamber II and a maximum permissible gas velocity thru the latter, sothat there is created in the gas stream passing thru inlet opening 34 agas velocity high enough to prevent the presence of dust in theimmediate vicinity of neck 34 and the connection thereof with the gaschamber. For this purpose, the material outlet end of the drum isprovided with a section 38 connecting the end of the drum to the drumneck 33. While section 33 may be cylindrical and coextensive with neck33, in which case section 38 connects with the vertical end wall 39 ofthe drum at a right angle, preferably section 38 is conical andapproximately of the configuration shown on the drawing. The conicaldesign of section 3B along with the restricted cross-sectional area ofdrum throat 33 provide a Venturi tube effect which facilitatesmaintenance at the gas inlet end of the drum of a relatively high gasvelocity. It has been found that, in order to create in the gas streamentering the drum a gas velocity high enough to prevent the presence ofdust in that vicinity, the vcross-sectional area of the drum throat 33should not be more than about one third the cross-sectional area ofdrying chamber II. Further, when using a conical connecting section 38,to create the most desirable Venturi tube effect and secure the bestresults, it has been found that the area of the circle formed by theintersection of connectionv 38 and drum wall 39 should be not more thanhalf the cross-sectional area of chamber Il, and that the axial lengthof section 38 should be equal to at least half the diameter of opening34.

Another'feature of the invention provides for removal of the drymaterial from the drum in such a way that the material being dischargedis out of contact with the gas stream entering thru opening 34. Thisobjective is-accomplished by a conveyor the tube of which is .supportedin the position shown on the drawing by a suitable bracket 46 and theend wall 41 of gas chamber 30. Tube 45 houses a screw 49 driven by amotor 50 and opens at the discharge end into an elevator conduit 5I orother receptacle. The closed portion of the tube 45 extends into dryingchamber II far enough so that material being discharged by conveyor 49is out of contact with gas in the zone of high gas velocity. The innerend of tube 45 is provided with an open top trough 54, the design ofsuch trough and of flights 22 being such that, during normal rotation ofthe drum, those portions of flights 22 adjacent the solid materialoutlet end of the drum keep trough 54 filled with dry material.

Assuming use of air as the drying agent, operation is as follows: Air isdrawn into the system by blower 24 and passed successively thru asuitable filter or purifier 26 and a heater 21 in which the air isheated to the desired drying temperature. Valve 29 in pipe 2B isadjusted so as to maintain heated air in the gas inlet chamber 30 undersuch a positive pressure that the velocity of the gas stream passingthru drying chamber Il does not exceed or is less than the maximumpermissible value, specific velocity being dependent upon thecross-sectional area of chamber I I and the nature of the material beingdried. By the construction described, there is thus created in thevicinity of the drum throat and of the connection between the same andthe fixed gas chamber 30, a gas velocity which is high enough to keepdust back in the drying chamber and well away from the gas inlet zoneformed by the conical section 38, drum throat 33 and the non-gas-tightconnection between the throat and gas inlet chamber 30. The positivepressure existing in chamber 30 maintains a small outflow of gas at theconnection lbetwen the rotary drum and the 'fixed gas chamber andprevents ingress of atmospheric air.

Following is an example of operation in which the material dried wasanhydrous bisuliite of soda containing about 5% by Weight of water asfed into the rotary drum. 'I'he length of the cylindrical portion of thedrum was 40 feet. The axial length of section 38 was 18 in., and theinside diameter of drum throat 33 was 24 inches. The cross-sectionalareas of drying chamber II, of the circle of intersection of end wall 39and conical connection 38, and of gas inlet opening 34 were 19.6, 7, and3.1 square feet respectively. Air was cleaned in purifier 26 by passingthru glass wool and cloth lter, and heated in heater 21 to an initialdrying temperature of 95 C. Blower 24 and-valve 29 were adjusted so asto maintain the gas in chamber 30 at a positive pressure of 0.2 in.(water). This pressure created an average gas velocity in thecylindrical section of drying chamber I I of about feet per minute,which gas velocity was low enough to avoid substantial entrainment ofdust in the spent gas discharged from the dryer. Under these conditions,the solid material was dried at a rate of 1.5 tons per hour, and therewas no discernabie leakage of dust at the non-gas-tight connectionbetween the drum and the fixed gas chamber 30.

I claim:

1. Apparatus for treating solid material at least some of which existsas dust when in the treated condition, which apparatus comprises arotary drum forming a treating chamber and having-a material inlet-gasoutlet end and an; oppositely disposed material dicharge-gas inlet.

end, means for introducing solid material to be treated into saidmaterial inlet end of said chamber. means for moving the material thrusaid chamber to said gas inlet end, an annular wall xed at its outerperiphery to said gas-inlet end of said drum, a frusto-conical sectionof substantial axial length having open ends one of which is larger thanthe other, the large end of said section being fixed to the innerperiphery of said wall, and the small open end of said section having across-sectional area not more than onethird that of said chamber, saidsection forming a gas inlet chamber for said treating chamber, a gasreservoir chamber communicating with the small end of said section andassociated therewith by a non-gas-tight eccentric-motion-permittingjoint, means for supplying treating gas to said reservoir chamber underpositive pressure to thereby supply gas under positive pressure to saidgas inlet chamber and to said treating chamber, and means fordischarging treated material from said treating chamber thru said gasinlet chamber While out of contact with a gas stream passing thru suchinlet chamber.

2. Apparatus for treating solid material at least some of which existsas dust when in the treated condition, which apparatus comprises arotary drum forming a treating chamber and having a material inlet-gasoutlet end and an oppositely disposed material discharge-gas inlet end.means for introducing solid material to be treated linto said materialinlet end of said chamber, means for moving the material thru saidchamber to said gas inlet end, an annular wall fixed at its outerperiphery to said gas-inlet end of said drum, a frusto-conical sectionhaving open ends one of which is larger than the other, the large end ofsaid section being ilxed to the inner periphery of said wall and havinga crosssectional area not more than half that of said chamber, and thesmall open end of said section Y having a cross-sectional area not morethan onethird that of said chambensaid section having an axial lengthequal to at least half the diameter of said small end and forming a gasinlet chamber for said treating chamber, a gas reservoir chambercommunicating with the small end of said section and associatedtherewith by a non-gas-tight eccentric-motion-permitting joint, meansfor supplying treating gas to said reservoir chamber under positivepressure to thereby sup- Iply gas under positive pressure to said gasinlet chamber and to said treating chamber, and means for dischargingtreated material from said treating chamber thru said gas inlet chamberwhile out of contact with a gas stream passing thru such inlet chamber.

3. Apparatus for treating solid material` at least some of which existsas dust when in the treated condition, which apparatus comprises arotary drum forming a treating chamber and having a material inlet-gasoutlet end and an oppositely disposed material discharge-gas inlet end,means for introducing solid material to be treated into said materialinlet end of said chamber, means for moving the material through saidchamber to said gas inlet end, an annular wall fixed at its outerperiphery to said gas-inlet end of said drum, said wall having afrusto-conical section of substantial axial length having open ends oneof which is larger thanthe other, the large end of said section beingrelatively adjacent said gas inlet end of said drum and the small end ofsaid section being relatively remote from said gas inlet end of saiddrum, the small open end of said section having a cross-sectional areanot more than one-third that of said chamber, said section forming a gasinlet chamber for said treating chamber, a gas reservoir chambercommunicating with the small end of said section and associatedtherewith by a non-gas-tight eccentric-motion-permitting joint, meansfor supf plying treating gas to said reservoir chamber under positivepressure to thereby supply gas under positive pressure to said gas inletchamber and to said treating chamber. and means for discharging treatedmaterial from said treating chamber while out of contact with a gasstream passing through such inlet chamber.

JOHN E. PEIRCE.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS OTHER, REFERENCES The Link-Belt Roto-Louvre Dryer,Book No. 1911. Copyright 1941 by Link-Belt Company. Pages 4,5, 14 and15.

